Dual mode satellite cellular telephone systems

ABSTRACT

A dual-mode telephone with a satellite communication adapter is disclosed. According to one embodiment of the present invention, a cellular-type handportable phone is equipped with a connector for the attachment of accessories. This connector provide a satellite communications adapter accessory access to the handset&#39;s signal processing resources which may operate in an alternative mode to process signals received from the satellite and converted by the adapter into a suitable form for processing. The processing translates the satellite signals into voice or data, and vice-versa.

FIELD OF THE DISCLOSURE

[0001] The present invention relates to the construction of portablewireless communication devices, and in particular to portable wirelesscommunication devices for communicating through orbital satellites.

BACKGROUND OF THE DISCLOSURE

[0002] Prior art-satellite terminals are large and expensive. Forexample, a terminal conforming to the standards known as INMARSAT-M isabout the size of a small suitcase and costs approximately $10,000 in1993. Such a terminal comprises a deployable directional antenna thathas to be pointed to the satellite with no intervening obstruction inthe line-of-sight, a telephone handset, and a box of electronics andbatteries which is coupled to the antenna and to the handset by wires.

[0003] Cordless telephones are well known in the domestic context, andallow a user more freedom of movement than conventional telephones.Cellular telephones extend the benefits of wireless communications overwide areas, and can be used in moving vehicles. U.S. patent applicationSer. No. ______, filed Nov. 4, 1993 describes an inventive combinationof cellular and cordless phone technology which allows the same,cellular handportable telephone to be used both in the wide-area, mobilecontext, and as a home cordless phone. In addition, the telephone canreceive calls either via the cellular system or via the normal hometelephone system. In the latter case, the calls are translated tolow-power cellular telephone call signals which can be broadcast usingthe same frequency bands as the wide-area cellular system withoutcausing interference.

[0004] The above systems do not disclose translating calls from asatellite communications system into low power cellular call signals inorder to receive them using a normal cellular handset.

[0005] U.S. patent application Ser. No. 07/967,027 discloses a dual-modecellular phone capable of operating in an analog FM mode oralternatively in a TDMA Digital speech mode, by using alternative signalprocessing programs in a programmable digital signal processor. In bothcases, the FM or TDMA signal to be processed is received over the airusing the same radio hardware.

[0006] U.S. patent application Ser. No. ______, filed on Sep. 14, 1994and entitled “Dual-Mode Satellite/Cellular Phone With A FrequencySynthesizer” describes a dual-mode satellite/cellular telephone thatcomprises a satellite RF processing section, a cellular RF processingsection, and a common signal processing section that can operate toprocess either satellite or cellular signals. This device lockspreferentially to landcellular signals, if available, and if not,alternatively to satellite signals.

[0007] The systems described above, however, do not describe a dual-modesatellite-cellular phone comprising a cellular handset adapted tointerface with a satellite adapter unit, wherein said handset receivessignal for processing from said adapter unit by means of suitablecables.

SUMMARY OF THE DISCLOSURE

[0008] It is an object of the present invention to provide a dual-modetelephone with a satellite communication adapter. According to oneembodiment of the present invention, a cellular-type handportable phoneis equipped with a connector for the attachment of accessories.According to the present invention, this connector provide a satellitecommunications adapter accessory access to the handset's signalprocessing resources which may operate in an alternative mode to processsignals received from the satellite and converted by the adapter into asuitable form for processing. The processing translates said satellitesignals into voice or data, and vice-versa.

[0009] The present invention provides a number of options. First, thepresent invention provides a low cost option involves omittinglandcellular-related components from the handset to provide the lowestcost satellite-only communications device. A second option comprises asecond adapter similar to that described in U.S. patent application Ser.No. ______, Filed on Nov. 4, 1993 and entitled “Home Base Station”,which is incorporated herein by reference, additionally equipped withthe interface to the satellite adapter. This adapter translates receivedsatellite signals into cellular-type signals which are rebroadcast forreception by the handportable cellular phone, and vice-versa. A thirdoption comprises connection of said “Home Base Station” also to thePublic Switched Telephone Network via a normal telephone jack outlet,such that calls received either via the satellite or via the PSTN aretranslated into cellular-type or wireless calls to the handset.

[0010] According to one embodiment of the present invention, a dual-modetelephone device for communicating either through an orbiting satelliteor through a landcellular system is disclosed. The telephone deviceincludes a cellular telephone unit adapted for communicating in acellular telephone network and further adapted to generate and toprocess digitized signals corresponding to transmissions to and fromsaid satellite. In addition, the telephone device comprises satellitecommunications adapter means for receiving signal transmitted by thesatellite and converting them to said digitized signals for processingby the cellular telephone unit and for receiving said digitized signalsfrom said cellular telephone unit and converting them to transmissionsto the satellite.

[0011] According to another embodiment of the present invention, asatellite communications adapter means is disclosed. The adapter meanscomprises directional antenna means and means for pointing saiddirectional antenna means toward an orbiting satellite. Transmit-receiveconnection means connect the antenna to receiving and transmittingcircuits. The adapter further comprises receive downconverting meansadapted to receive a satellite signal via the transmit-receiveconnection means and to process them into a form for connection to ahandset using a flexible cable. Transmit modulation and amplifying meansare also provided for receiving complex modulating signals from thehandset using the flexible cable and for upconverting them andamplifying them for transmission using the directional antenna to thesatellite.

DETAILED DESCRIPTION OF THE DRAWINGS

[0012] These and other features and advantages of the invention will bereadily apparent to one of ordinary skill in the art from the followingwritten description, used in conjunction with the drawings, in which:

[0013]FIG. 1 illustrates a dual mode satellite-cellular phone;

[0014]FIG. 2 illustrates a frequency plan for 5 KHz channel spacing inthe satellite mode;

[0015]FIG. 3 illustrates a dual mode phone according to one aspect ofthe present invention;

[0016]FIG. 4 illustrates a wireless adapter according to the presentinvention;

[0017]FIG. 5 illustrates serial data formats conforming to the presentinvention;

[0018]FIG. 6 illustrates serial data submultiplex format according tothe present invention;

[0019]FIG. 7 illustrates a single wire pair interface according to thepresent invention; and

[0020]FIG. 8 illustrates a wireless connection to a cellular handsetaccording to the present invention.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0021] The operation of a satellite-cellular portable phone according toU.S. patent application Ser. No. ______, entitled “Dual-ModeSatellite/Cellular Phone With A Frequency Synthesizer” which isexpressly incorporated herein by reference, is explained with the aid ofFIG. 1. A cellular transmitter-receiver RF circuit 10, which may, forexample, be adapted to the European GSM standard operating atfrequencies of 900 MHz (Europe), 1800 MHz (UK DCS1800 system) or 1900MHz (U.S.) is connected to a cellular antenna 11. The followingdescription is based or the cellular mode conforming to the 900 MHz GSMstandard, but this is merely exemplary and any cellular standard can beused for the present invention. A synthesizer 34 supplies a localoscillator signal to the cellular-mode RF circuits in the range1006-1031 MHz in 200 KHz steps which is derived by dividing the outputof a 13 MHz reference oscillator 12 by 65 in divider 22. A phasedetector 24 compares this 200 KHz reference signal with the output of aVCO 30 divided by a variable integer N1 in a divider 26. The phase errorfrom a phase detector 24 is filtered in a loop filter 29 and thenapplied to a control VCO 30 such that its frequency is N1 times 200 KHz.

[0022] The GSM receiver part of the cellular transmitter-receiver RFcircuit 10 in this example converts received signals first to anintermediate frequency of 71 MHz by mixing with the synthesized localoscillator frequency and then to a second intermediate frequency of 6MHz by mixing with 65 MHz, which is 5 times the 13 MHz reference. Thesecond IF signal is processed to extract an RSSI signal which isapproximately proportional to the logarithm of the amplitude. This canbe done either by using a radar-type logarithmic IF amplifier or by useof a fast, automatic gain control. In the former case, a hardlimited IFoutput is also obtained from which amplitude variations have beenerased; in the latter case, an amplitude-controlled output is obtained,from which amplitude variations have been substantially reduced by theautomatic gain control. The former case is the preferred implementation,in which a hardlimited IF signal is produced.

[0023] The IF output signal is processed in an AtoD convertor 13 toextract numerical values related to the instantaneous signal phase, forexample, COS(PHI) and SIN(PHI) and these are combined with the result ofanalog-to-digital conversion of the RSSI signal and transferred viainterface circuits 14 to the digital signal processing circuits 15. Asuitable method of performing the above radio signal digitization isdisclosed in U.S. Pat. No. 5,048,059, filed Sep. 18, 1989, which isincorporated herein by reference. The signal is processed to form PCMvoice samples which are transferred back via interface circuits 14 tothe DtoA convertor 13 and then to an earpiece 19.

[0024] In the cellular transmit direction, a microphone 20 suppliesvoice signals to the AtoD convertor 13 where the voice signals becomedigitized and transferred via interface circuits 14 to digital signalprocessing circuits 15 for coding. The coding reduces the bitrate fortransmission and the reduced bitrate signal is transferred back throughinterface circuit 14 where it is converted into I,I,Q,Q modulatingsignals. The modulating signals are fed to the GSM transmitter-part ofthe RF circuit 10 where they are converted to the 890-915 MHZ range fortransmission via an intermediate frequency of 117 MHz, which is 9 timesthe 13 MHz reference frequency.

[0025] The control and interface circuits 14 also contain amicroprocessor coupled to a RAM 18, a flash program memory 16 and anEEPROM 17, as well as to a man-machine interface 35 which may, forexample, be a keypad and display. The RAM 18 may be used in a sharedfashion by the microprocessor and by the digital signal processingcircuits 15 according to the advantageous method disclosed in U.S.patent application Ser. No. 08/143,640, entitled “Multiprocessor RAMSharing”,which is incorporated herein by reference.

[0026] In the GSM mode, the satellite communications circuits 21 arepowered down by control signals from the control interface circuit 14 tosave power, as are other unused parts of the dual-mode synthesizer, suchas the VCO 31. Many other battery-power saving features are alsoincorporated, and in particular the phone when in standby mode can bepowered down for most of the time and only wake up at predeterminedinstants to read messages transmitted by GSM base stations in itsallocated paging time slot.

[0027] When the phone, in idle mode, detects that all GSM base stationsare becoming weak, the phone employs idle time between GSM wakingperiods to activate the satellite circuits to search for a satellitecalling channel signal. The satellite receiving circuits 21 receive alocal oscillator signal from a synthesizer 34. By mixing with thesynthesizer's second output, the satellite receiver circuits convertreceived signals to a first intermediate frequency (IF) of 156.45 MHzand then to a second IF of 450 KHz by mixing with 12 times the 13 MHzreference. The satellite mode channel spacings in this example are (13MHz/64×65-3.125 KHz). The second IF is hardlimited and processed toextract an RSSI signal approximately proportional to the logarithm ofthe signal amplitude. The hardlimited IF is further processed in thecontrol and interface circuit 14 to extract signals related toinstantaneous signal phase. These are combined with digitized RSSIsignals from the AtoD converter 13 and passed to the digital signalprocessing circuits (15) where they are processed to detect satellitesignals. If satellite signals are detected and GSM signals are weak, thephone sends a deregistration message to the GSM system and/or aregistration message to the satellite. These aspects are described inU.S. patent application Ser. No. 08/179,958, entitled “PositionRegistration For Cellular Satellite Communication Systems”, which isincorporated herein by reference.

[0028] Upon deregistration from GSM, the GSM circuits in the phone areturned off and the satellite receiver and relevant parts of thesynthesizer are powered up to listen to the narrowband satellitecontrol/paging channel. Preferably this channel is also formatted insuch a way that the receiver only needs to power up to receive aparticular timeslot assigned for paging that mobile phone. Thisconserves battery power in idle mode, especially if fast synthesizerlock times from momentary power up can be achieved. Moreover, some ofthe spare time between paging slots in the satellite format can bedevoted to scanning GSM frequencies for the re-appearance of a GSM basestation signal, which would trigger a reversion to the cellular mode.The cellular mode is the preferred mode since it is desirable tominimize the number of subscriber telephones that use thecapacity-limited satellite system at any one time. In this way, only asmall percentage of phones temporarily outside of cellular coveragerepresent a potential load on the satellite capacity, so the number ofdual-mode phone subscribers can be many times greater than the capacityof the satellite system could support.

[0029] Because of the difficulty of obtaining a reference frequencyoscillator of adequate stability, small size, and low cost for aportable phone, it is customary to utilize the base station signal as areference and to lock the phone's internal reference frequency to thereceived base station signal by generating an AFC signal as shown inFIG. 1 as “voltage control” from the DtoA convertor 13 to the referenceoscillator 12.

[0030] The above system description was based on a 3.125 KHzchannel-spaced satellite mode. This is determined by the divider valuesof dividers 22 and 23, in this case 65 and 64, respectively. The firstdivider ratio arises due to GSM bitrates being based on a 13 MHzreference clock which is 65 times the channel spacing. For a Vernierloop synthesizer, the second divider ratio is 1 away from the first,i.e., 64 or 66. A divider ratio of 64 in this case is a rational choice.

[0031] It is also possible to configure the dual-mode phone describedabove for 5 KHz satellite mode channel spacing. In this case, a 39 MHzreference oscillator may be used. This embodiment is shown in FIG. 2,where only RF circuitry and the synthesizer are shown. The basebandelements 13, 14 and 15 remain as previously described.

[0032] The 39 MHz reference oscillator 52 is divided by 39 and 40 indigital dividers 50 and 51, respectively. The divider 50 thus produces a1 MHz reference frequency for a phase comparator 48. A first VCO 40which produces a local oscillator suitable for the GSM mode, is dividedby N1+dN1 in a fractional-N divider 43 operating as disclosed in U.S.patent application Ser. No. 07/804,609. The value dN1 can be programmedfrom 0 to ⅘ths in steps of ⅕th so that VCO 40 is controlled to be N1+dN1times 1 MHz in 200 KHz steps.

[0033] A second VCO 41 operates to generate a suitable local oscillatorsignal for the satellite mode. It is mixed down to the 280-300 MHz rangeagainst a VCO 50 in a mixer 42 and then after low-pass filtering in afilter 45 is divided in a divider 44 by N2+dN2 in steps of ⅕th. Thedivided output is compared in a phase detector 49 with the output of thedivider 51 and the error signal from 49 is filtered in a loop filter 46before application to the control VCO 41 such that its frequency is(N2+dN2)39 MHZ/40+VCO(50) frequency.

[0034] Thus, the frequency of VCO 51 is given by${\lbrack {\frac{n1}{39 \times 5} + \frac{n2}{40 \times 5}} \rbrack \times 38\quad {MHz}} = {{\frac{{5 \times 40 \times {n1}} + {5 \times 39 \times {n2}}}{39 \times 5 \times 40 \times 5} \times 39\quad {MHz}} = {{40{n1}} + {39{n2} \times 5\quad {KHz}}}}$

[0035] where n1=5(N1+dN1) and n2=5(N2+dN2). Thus, by varying theintegers n1 and n2, frequencies can be generated in 5 KHz steps, asrequired for the postulated narrowband satellite mode. This desiredbehavior was obtained using a combination of fractional-N and VernierLoop techniques to achieve both 200 KHz and 5 KHz steps simultaneouslyat respectively cellular and satellite frequency bands. Both synthesizerloops operate with reference frequencies around 1 MHz and can have wideloop bandwidths to suppress phase and frequency noise and to achievefast frequency switching times.

[0036] The output of the VCO 40 between 1085 MHz and 1110 MHz mixes withthe GSM received signals in the band 935-960 MHz to generate a 150 MHzfirst intermediate frequency (IF). This is chosen deliberately so thatthe second local oscillator of 156 MHz used to convert the first IF to asecond IF of 6 MHz is a simple multiple (×4) of the 39 MHz referencefrequency crystal, produced by a frequency multiplying circuit 53.Alternatively, it can be advantageous to use a 156 MHz crystal referenceoscillator and instead to divide it down by 4 to generate the required39 MHz. As another alternative, any frequency multiplying circuit can ofcourse be implemented with the aid of either a harmonic generator plusharmonic selection filter, or with the aid of a simple phase lock loop.It will be noted that the second local oscillator is chosen to be thesame frequency for the cellular and satellite receiver sections foreconomy.

[0037] The satellite receive section 55 effects amplification andfiltering of the satellite received signal band of 1525-1559 MHz whichis then mixed down against the VCO 41 output to generate a fixed IF of156.45 MHz. This is further mixed down against the 156 MHz second localoscillator to generate the final IF of 450 KHz. It is also possible touse the more standard 455 KHz by merely programming the satellitesynthesizer one 5 KHz step lower in frequency and choosing the first IFto be 156.455 MHz.

[0038] The final IFs of either 6 MHz (GSM) or 450 KHz (satellite) aredigitally processed as previously described. The digital processing canbe supplied with a 13 MHz clock, from which all GSM bitrates and frameperiods derive, by dividing the 39 MHz reference frequency by 3 using adivider 56.

[0039] Further description of this prior invention, such as transmitprocessing, may be found in the above-referenced patent applicationwhich was incorporated herein above.

[0040] This prior invention was conceived to provide a dual-mode,satellite-cellular phone that switched between satellite and cellularmodes according to signal availability, which is a function of mobileposition. An implicit requirement of satellite-to-handportable or mobilecommunications is that the satellite be powerful enough to communicatewith phones having arbitrarily oriented antennas, i.e., omnidirectionalantennas.

[0041] On the other hand, the present invention aims to provide asatellite link using existing satellites of limited power, which requirea directional antenna to be used at the telephone terminal. The presentinvention is not therefore concerned with solving the problem ofproviding a dual-mode phone which automatically switches betweensatellite and cellular modes according to signal availability changingdue to moving position, but rather is concerned with providing adirectional antenna for a satellite mode, the mobility of which isrestricted due to the antenna being inherently large, and to the needfor the antenna to be pointed at the satellite. It is clearly notappropriate to attach such an antenna to the telephone handset which islifted to the user's ear. On the other hand, this was appropriate in thecase of the previous invention where a small omni-directional antennasufficed.

[0042] One solution would be to employ a stand-alone antenna connectedto a handset according to the prior invention by means of a coaxialcable. However, the diameter of a coaxial cable with sufficiently lowloss at around 2 GHz is inconvenient. The cable size could be reduced byincluding a low-noise amplifier as part of the antenna for the receivedirection. The transmit direction also requires low loss and so thetransmit power amplifier should preferably also be located in theantenna, as then must the transmit-receive duplexing filter in the caseof a frequency-duplex system. However, two coaxial cables are thenneeded to carry separately the output of the low noise amplifier to thehandset as well as the power amplifier drive signal from the handset.

[0043] The above dilemma is solved by configuration of a satellitecommunications adapter according to the invention which will now bedescribed with reference to FIG. 3.

[0044] A directional antenna 500 is connected via a duplexer or atransmit/receive switch 107 to receive processing circuits 100 andtransmit circuits 200. The unit 107 is appropriately a duplexing filterfor frequency duplex systems or a T/R switch for time-duplex systems.The receive processing circuits 100 convert received satellite signalsto a low intermediate frequency, for example 450 KHz, using adouble-superheterodyne comprised of a low noise amplifier 101, an imagerejection filter and mixer or image rejection mixer 102, first IFfilters and amplifiers 103, a second mixer 104 and second IF filters andamplifiers 105. A balanced output from the second IF amplifier assistsin avoiding unwanted feedback to the input of the high gain second IFamplifier. A transformer 106 may optionally be used to interface thebalanced IF signal to a cable for connection to remote signalprocessing.

[0045] The transmitter comprises a transmit signal generator 300 and atransmit power amplifier 200. The transmit configuration illustratedhere is a version for constant-envelope signals, as versions for bothconstant envelope and varying amplitude signals were disclosed in theaforementioned prior application which has already been incorporatedherein by reference.

[0046] The constant envelope transmit circuit generates the purely phasemodulated signal first at a convenient transmit IF produced by a TXIFgenerator 306 and modulated using a quadrature modulator 305. The poweramplifier 200 comprises its own transmit frequency voltage controlledoscillator 202 which drives a power amplifier 201. A sample of the VCO202 signal is downconverted to the convenient TXIF by mixing in a mixer301 with a local oscillator signal produced by a synthesizer unit 400.The TXIF signal from the mixer 301 is compared with the modulated TXIFsignal from the modulator 305 using a phase detector 303 to produce aphase error signal. The phase error signal is filtered using a loopfilter 203 to produce a control signal for the VCO 202 which controlsthe VCO phase and frequency to follow closely that of the modulatedTXIF. Thus, the modulation is transferred to the VCO's output signal andhence to the amplified output of the power amplifier PA 201.

[0047] The frequency synthesizer unit 400 is programmable by means of aserial digital control stream to generate various receive and transmitLocal Oscillator frequencies so that the inventive adapter operates onallocated frequencies in the satellite transmit and receive bands,respectively. These frequencies are generated with the help of a crystalreference frequency produced by a crystal 206 and an oscillator 307, anynecessary buffer amplifiers or frequency multiplications necessary todrive the synthesizer being implicitly contained in block 306. Forexample, a 13 MHz crystal could be used, and block 306 can comprises aTXIF synthesizer as well as a times 3 multiplier to produce a 39 MHzreference for the synthesizer unit 400, which can employ the inventivevernier-fractional-N principle disclosed in the aforementionedapplication. The crystal oscillator furthermore is controllable infrequency over a small range by means of a varactor diode 207 connectedto an AFC control line. The purpose of this is to compensate for crystalfrequency tolerances and temperature variations.

[0048] It is disclosed in U.S. patent application Ser. No. 07/967,027and claimed in Continuation application Ser. No. ______, filed Sep. 14,1994 and entitled “Quadrature Modulator With Integrated Distributed RCFilters”, that a quadrature modulator may advantageously employ balancedI,Q input drive signals. These four signals denoted in FIG. 3 by I,I,Q,Qcomplete the definition, apart from possible ground pins, powersupplies, on/off control etc., of the principal signals forminginterface 600 with remote signal processing located in the handset.

[0049] An inventive interface between a satellite RF adapter and ahandset containing signal processing according to the above descriptioncomprises one embodiment of the present invention. An interfacecomprised of say 12 pins, all signals being of low bandwidth and ofconvenient levels is a reasonably practical solution. Reducing pin countis always a design goal however as there may be other functions notconsidered above that have from time to time to be accessed through thesame connector, such as plugging the handset into a charger or acellular vehicular adapter. Furthermore, an inventive interface of thefirst type has not addressed the AFC problem of a dual-modecellular-satellite phone, a solution for which is disclosed in U.S.patent application Ser. No. ______, filed Sep. 14, 1994 and entitled“Frequency Error Correction In a Satellite-Mobile CommunicationsSystem”, which is incorporated herein by reference. This discloses adual-mode terminal having a single reference frequency crystaloscillator which is controlled to an exact frequency by measuring afrequency error from the cellular system, so that the frequency isalready nearly correct when attempting to access the satellite system,or alternatively locks to the satellite system and determines afrequency error and a Doppler shift due to satellite motion, and aftercompensating said Doppler shift adjusts said reference frequencyoscillator to a correct absolute frequency for later accessing thecellular system. In the present invention, however, there may beseparate reference frequency oscillators for satellite and cellularmodes. A reference oscillator must be included in the handset if it isintended to function as a wireless telephone when not connected to thesatellite adapter. It is possible to feed this reference oscillator fromthe handset to the satellite adapter using another wire but this is ahigh frequency signal and so it may be undesirable. Nevertheless, itwould be desirable to be able to ensure that a separate referenceoscillator in the satellite adapter could be adjusted to the sameabsolute accuracy as the reference oscillator in the handset, so thatthey behaved as one frequency reference capable of being updated eitherby receiving a cellular or a satellite signal, as disclosed in theaforementioned disclosure which is incorporated herein by reference.

[0050] An alternate inventive interface is now described with the aid ofFIG. 4 which aims to reduce the pin count and also to provide a means tosynchronize separate reference oscillators. FIG. 4 illustrates amultiplexing/demultiplexing circuit that may be included in theinventive satellite communication adapter to reduce the number of wiresneeded to connect the adapter to the handset. The multiplexing circuit601 connects to the previously described interface 600 on the left ofFIG. 4. The received signal strength measure denoted by RSSI isconverted from an analog waveform to numerical samples by sampling anddigitizing using an AtoD convertor 602. The hardlimited IF output fromsecond IF amplifier 105 contains phase information which is extracted,for example, by means of a direct phase digitizer 603 that can operateaccording to the principles disclosed in U.S. Pat. Nos. 5,084,669 or5,220,275, which are both incorporated herein by reference.Alternatively, phase-representative information can be extracted fromthe saturated IF output in the form of numerical values of the cosineand sine of the instantaneous phase, as disclosed in U.S. Pat. No.5,048,059 which is also incorporated herein by reference. The latter maybe extracted by, for example, low-pass filtering the IF output to obtaina sinusoidal waveform and then quadrature sampling it by digitizingsample pairs taken nominally ¼ cycle apart. U.S. Pat. No. 5,048,059discloses how the RSSI or logamplitude signal may be processed togetherwith the phase-related signals to preserve the complex vector nature ofthe signal. In the following, it is assumed that a phase digitizer 603outputs in 8-bit phase samples and that RSSI digitizer 602 outputs in8-bit logamplitude samples, however the present invention is not limitedthereto, which could equally well be configured to use Cartesian (I,Q)digitization of received signals. The method of digitizing the receivedsignal is a matter of design choice, but the logpolar method of the U.S.Pat. No. 5,048,059 is the preferred method. The digitized receivedsignal samples are multiplexed together with other bits by a multiplexer607 to obtain a single serial digital stream for sending to the handset.The other bits multiplexed by the multiplexer 607 can be status bits orechos or acknowledgements of information or commands received on thebit-serial link from the handset. Such looped-around bits can be used bythe handset to detect whether the inventive adapter is connected andperforming as expected.

[0051] The serial link from the handset carries multiplexed informationcomprising the I and Q modulation samples, AFC words for the DtoAconvertor 604, frequency setting words for synthesizer(s) 400 andcontrol bits for the multiplexer and timing generator 607. The controlbits can, for example, be used to program particular sample times orsample rates for the logpolar digitizer 603.

[0052] The I,Q samples received by a demultiplexer 606 over thebit-serial link are a complex numerical representation of the modulatedsignal to be transmitted to the satellite. This signal may be adigitally modulated signal using QPSK or Offset QPSK, for example. Thesample rate of the I,Q streams must be at least the Nyquist rateappropriate to the I,Q signals' bandwidth, but is preferably many timeshigher (e.g., 4 to 40 times) in order to simplify filters 204 and 205which attenuate sample rate components while passing the signalbandwidth. In order to avoid an excessive bitrate for the serialbitstream, this so-called oversampling factor can be kept to a modestvalue such as 5, and a converter 605 can comprise upsampling orinterpolation to raise the oversampling rate locally. The main functionof the Delta-Sigma convertors 605 is, however, to assist in theconversion of the digital I,Q sample streams to separate, analog I,Qmodulating waveforms. This is done by converting the I and Q samplestreams first to high bitrate delta-sigma bitstreams that represent theI,Q values by the proportion of 1's or 0's that the streams contain. Amaximum level I signal would consist of continuous 1's (100% dutyfactor) while the maximum negative value would be continuous 0's.Because between 1 and 0 there is no negative voltage, the I and Qstreams are each converted into two complementary streams I,Q and I,Qthat each have a duty factor lying between 0 and 100% but which varyinversely. The I signal is then represented in the difference in dutyfactor between the I and the I stream, and Q likewise. This method ofconverting I,Q numerical samples to analog waveforms for modulating aquadrature modulator is described in U.S. Patent application filed Sep.14, 1994 and entitled “Quadrature Modulator With Integrated DistributedRC Filters”, which is incorporated herein by reference. The advantage ofhigh bitrate delta-sigma conversion is that low-pass filters 204 and 205are simplified. The advantage of the balanced form of delta-sigmaconvertor and low pass filters disclosed in the incorporated applicationis to reduce unwanted carrier components in the modulated output causedby DC offsets.

[0053]FIG. 5 illustrates a suitable serial bitstream format for thehandset to adapter and from the adapter to the handset. 25-bit words aretransmitted at a 40 Kword/sec rate giving a Imbit stream, derived fromthe handset reference crystal in the handset-to-adapter direction andfrom the adapter reference crystal in the adapter-to-handset direction.The 25-bit word consists normally of a start bit or flag equal to binary1, an 8-bit sync pattern and 8-bit 1 and 8-bit Q values. The I and Qvalues are transmitted at a rate of 40K samples per second, which is 5times an 8 KB/s modulated bitrate carried by the I and Q waveforms, orten times the Nyquist rate assuming QPSK modulation. By making the flagbit alternatively a binary 0, the handset indicates as illustrated inFIG. 6 that the sync bits instead carry command information 8-bits at atime. By holding the flag at 0 for however many consecutive 25-bit wordsas necessary, any number of bytes of command information may beconveyed. For example, commands can consist of 4 bytes, comprising an8-bit address (denoting a synthesizer for example) and 24 bits of data(denoting a frequency for example).

[0054] A similar format may be used in the reverse direction, where I,Qbytes are replaced by phase and amplitude bytes, and where command bytesare replaced by status bytes when the flag is a zero, as commanded byhandset-to-adapter commands.

[0055] Serial data streams containing multiplexed information must besynchronized at the receiving demultiplexer to determine the wordboundaries. It is not the purpose of the disclosure to describe suchprior art techniques. It suffices to say that the inclusion of flag bitsin regular positions with associated known sync patterns providessufficient data for the receiving demultiplexer to obtain synchronismusing known sync search techniques and to maintain synchronization usingknown flywheel sync techniques. The similarity of the format in bothdirections allows a similar synchronizing circuit design to be used atboth ends.

[0056] Another purpose of the inventive interface 700 however is tosynchronize the reference oscillator 307 accurately to the handsetreference oscillator, or vice versa. A clock comparator in thedemultiplexer 606 determines whether the rising or falling edges ofcorresponding bits transmitted and received over the serial links (e.g.,sync bits) are early or late with respect to each other. For example, ifthe first sync bit transmitted from the adapter through the multiplexer607 occurs later than the reception of the same bit through thedemultiplexer 606, then the adapter's reference is deemed to be runningslow and its frequency should be increased. It is an optional designchoice whether circuitry to compute a new code for the DtoA convertor604, is contained in the adapter, or whether such early/late decisionsare merely reported in the status bits transmitted to the handset, andthe computation to update the DtoA converter 604 code is contained inthe handset. Since it has also been indicated that a similar circuit tothe multiplexing circuit 601 may be suitable for inclusion in thehandset, it is possible alternatively for the handset circuit tocomprise comparison of transmitted and received bitstream timings inorder to determine early/late decisions which may then be used to updatethe DtoA convertor code transmitted to the adapter or used to update thehandset's internal reference oscillator. It is preferable to permit alloptions, and to determine whether the handset's or the adapter'sreference oscillator is the one to be adjusted depending on whether theformer has previously been adjusted to an accurate cellular base stationused as a frequency reference. The objective guiding the design oroperation of such an algorithm, which may comprise part of the handsetsoftware, is to obtain the best transmit frequency accuracy for asatellite mode transmission by using either previous cellular frequencyerror measurements or current satellite frequency error measurements,whichever is of greatest reliability. Moreover, temporary adjustments tothe handset reference are permitted by storing a DtoA convertor 604 codepreviously determined while locked to a cellular system, and retrievingit from memory when next locked to a cellular system. In this way,future frequency refinements to frequency adjustments to the satelliteor cellular system may be kept independent of each other.

[0057] Since an object of the invention was to simplify the connectionbetween the handset and the satellite adapter, the serial control clockshown accompanying serial control data on interface 600 was omitted frominterface 700 to save pins. However, if pins are available, a 1 MHZclock or alternatively a 40 KHz word strobe or both can be connectedbetween the handset and the adapter to simplify bit or wordsynchronization while retaining the spirit of the inventive satellitecommunication adapter. The different trade-offs between the numbers ofwires and the signal bandwidth or bitrate carried by each merelyrepresent different implementations. It is possible to multiplex bothdirections onto a single wire plus ground (or single pair) bytransmitting bursts of data alternately in each direction by using atime duplexer.

[0058] This final step of using time duplex along a single wireline pairis illustrated in FIG. 7. The interface circuit 701 contains a modifiedmultiplexer and demultiplexer 706 and 707 and a new bidirectionalwireline interface circuit 708. The modifications to the multiplexer anddemultiplexer 706 and 707 adapt them respectively to receive andtransmit alternate data bursts instead of continuous data. Toaccommodate for data in both directions, the serial bitrate must beraised to approximately double the previous 1 MB/s rate. A suitablebitrate is 13 MHz/5 which is equal to 2.6 MB/s.

[0059] A burst rate of 40 KHz in each direction is maintained. Eachgo-and-return cycle period contains 65 bit periods at 2.6 MB/s of which,for example, 25 bit periods may be used for transmitting data words inone direction and 25 bit periods for data words in the other direction,the data words conforming to the exemplary format of FIGS. 5 and 6. Theremaining 15 bit periods may be used for guard time between transmit andreceive bursts to allow the bidirectional line interface 708 to switchdirection. The early/late clock comparator contained in thedemultiplexor 706 operates as before, except that the timing of bitreception from the handset is compared with the internal timing of themultiplexer 707, which is the bit timing it would have used had it beenpermitted to transmit. The timing comparison effectively checks thatdata is received from the handset midway between the transmission of two25-bit words from the multiplexer 707 and generates an early or lateindication. To assist in initial sync or sync recovery, the multiplexer707 is inhibited from transmission if the demultiplexer 706 does notdetect synchronization with the signal from the handset.

[0060] The description so far has concentrated on wire connection of thehandset to the inventive satellite communication adapter. In U.S. patentapplication Ser. No. ______, a Home Base Station was disclosed fortranslating a call received via a normal, loop-disconnect interface withthe public switched telephone network PSTN through a domestic telephonejack outlet into a call to a cellular phone using a low powertransmitter, and vice versa. A call received from a cellular phone atlow power is translated by the Home Base Station into a normalloop-disconnect telephone jack interface with the PSTN.

[0061] According to one embodiment of the present invention, the HomeBase Station is equipped with an additional interface for connection tothe inventive satellite communication adapter. This interface can be anyof the interfaces described above and denoted as interfaces 600, 700 or800 respectively in FIGS. 3, 4 and 7. The common principle is that thesatellite communication adapter is principally just an RF convertor andrelies upon the Home Base Station's digital signal processing to processsatellite signals. Thus, signals received from the satellite andconverted by the adapter illustrated in FIG. 3 are fed to the Home BaseStation using signal interfaces 600, 700 or 800 and then processed intocellular signals which are transmitted by the Home Base Station to acellular handset, such as the handset disclosed above having saidinventive interface, or alternatively to any suitable cellular handset.Likewise, signals transmitted from said cellular handset are received bysaid Home Base and converted to satellite signals that are transmittedover the interface 600, 700 or 800 to the inventive satellitecommunication adapter for transmission to the satellite. In the eventthat the Home Base Station is also connected to the PSTN via aloop-disconnect telephone jack outlet, calls received either from thesatellite or via the PSTN may be translated to calls to the samecellular handset. In this way, the inventive satellite communicationadapter comprises a directional antenna that must be pointed at thesatellite can be set up at one location and used by a handset in anotherlocation by use of normal cellular circuits and transmission protocolsas a wireless connection. For handset initiated calls, the decision toplace them via the PSTN or the satellite can depend on availability anda priority indication provided by the user. For example, said Home BaseStation can be set to give priority to placing handset initiated callsvia the route offering the lowest tariffs. A local call would be placedvia the PSTN for example, while an international call may be placed viathe satellite system. Discrimination between local and internationalcalls may be made by the Home Base Station by processing the digits ofthe called number and referring to a table of user-programmed preferredrouting information. In addition, the handset may independently chooseto use a local cellular system if available as an alternative to thesatellite or PSTN routing options.

[0062]FIG. 8 illustrates these call routing options. The Inventive HomeBase Station 1001 is connected to the inventive satellite communicationadapter 1000 by means of any of the aforementioned interfaces. Since theHome Base Station is also conceivably a battery charger in which thehandset is parked when not in use, it may in principle also function asa power source or charger for the adapter 1000 by adding appropriatepower connections in the cable interface. The Home Base. Station drawspower from the power line for this function. The function of the HomeBase Station can comprise causing the handset to ring by non-radio meanswhen parked in the charge position, and performs a wireless call set-upwith the handset first upon detection that the handset is removed fromthe charger to answer the call. Alternatively, an interface with thenormal wireline phone is optionally provided, and calls may be made oranswered using the wireline phone by non-wireless communication with theHome Base/satellite communication Adapter combination. In thisconfiguration, whichever phone is picked up or answered first, thecellular handset or the normal phone, can determine whether a wirelessor wired connection is first activated.

[0063] If desired, the function of the Home Base Station can beprogrammed to activate the cellular wireless connection to the cellularhandset if it is later picked up subsequent to answering the calloriginally with the wireline phone. Other options such as allowing acall to be monitored both on the wireline phone and the wirelesshandset, regarded as separate extension phones can be programmed.Furthermore, a call answered using the wireline phone while the cellularphone is disconnected from the charging position, thereby terminatingthe radiation of a cellular call signal by 1001) can in principle bepicked up from the wireline phone later by the cellular phone throughdialling its number. The Home Base Station can be programmed torecognize cellular signals containing a call to the PSTN Jack it isconnected to and to connect those to the wireline phone directly, eitherfor talking with the wireline phone or for picking up an existing callto the wireline phone. Attempts to pick up a call from the wirelinephone can be either permitted or blocked, in the latter case by issuinga busy signal to the cellular handset.

[0064] It will also be appreciated by a person skilled in the art thatany of the inter-unit connections illustrated in FIG. 8 as beingcompleted with electrical cables can equally be accomplished usingoptical fiber. Such options and alternate interfaces between a satellitecommunication adapter, a cellular handset or a Home Base Stationdesigned by a person skilled in the art are all considered to lie withinthe spirit and scope of the invention as described by the followingclaims.

[0065] It will be appreciated by those of ordinary skill in the art thatthe present invention can be embodied in other specific forms withoutdeparting from the spirit or essential character thereof. The presentlydisclosed embodiments are therefore considered in all respects to beillustrative and not restrictive. The scope of the invention isindicated by the appended claims rather than the foregoing description,and all changes which come within the meaning and range of equivalentsthereof are intended to be embraced therein.

What is claimed:
 1. In a dual-mode satellite/cellular telephone systemincluding a cellular telephone, a satellite-cellular communicationsadapter, separate from said cellular-telephone, said communicationsadapter comprising: a converter for converting satellite signalsreceived from an orbiting satellite into information signals for use bysaid cellular telephone and for converting-information signals receivedfrom said cellular telephone into satellite signals for transmission tothe orbiting satellite; and an interface for connecting saidcommunications adapter to said cellular telephone and for communicatinginformation signals between said adapter and said cellular telephone,wherein information signals communicated via said interface saidcellular telephone to said adapter include balanced in-phase andquadrature drive signals, and wherein information signals communicatedfrom said adapter to said cellular telephone include an intermediatefrequency signal.
 2. An adapter according to claim 1, whereininformation signals communicated from said cellular telephone to saidadapter further include an automatic frequency change signal and aserial digital control signal, and wherein information signalscommunicated from said adapter to said cellular telephone furtherinclude a received signal strength indicator signal.
 3. An adapteraccording to claim 1, wherein said interface comprises a multi-pinconnector and electric cabling.
 4. An adapter according to claim 1,further comprising a multiplexing/demultiplexing circuit for combiningand serializing information signals communicated between said cellulartelephone and said communications adapter.
 5. An adapter according toclaim 4, wherein said interface comprises one of electrical cabling andfiber optic cabling.
 6. An adapter according to claim 4, furthercomprising a bi-directional line interface coupled to saidmultiplexing/demultiplexing circuit.
 7. An adapter according to claim 6,wherein said interface comprises a single twisted wire pair.